exporting procedural landscape
Using node based shaders and modifiers is something that is specific to blender, neither of these export well to other programs.

For node based materials, you can bake the shader nodes to an image that can be used in other programs. This only applies to the surface appearance; such as colour, specularity, glossiness...

A normal map used in a shader can also be used in other programs, but mesh displacement in shaders will not export.

When you are using a displacement modifier, as well as any modifier except armature, you will need to apply the result of the modifiers when exporting. Most exporters provide an option to do this for you during export. For gltf, look for the Apply Modifiers option, in 2.80 it is under General, in 2.81 it is under Geometry.